It is known to employ urea-formaldehyde/melamine formaldehyde resin solutions, and mixtures thereof, as binders for wood materials, such as chip boards, wood fiber boards, plywood etc. Although the urea-formaldehyde/melamine-formaldehyde resins are effective binders for wood, they have the great disadvantage in that they are unstable for a long period of time after treatment of the wood materials resulting in noxious formaldehyde odor and bound wood materials which do not give resistance to weather as required by German Industrial Standards (DIN) No. 68,761.
On the other hand, phenol-formaldehyde resin solutions have the great advantage of emitting essentially no formaldehyde and always meet the required weather resistance (DIN 68,761). However, the disadvantages of phenolic resins are their dark color and free phenol content of at least 10 ppm which introduces an unpleasant factor in working up the wood materials. In regard to the phenol content, the grinding dust of phenol-formaldehyde treated wood material containing, e.g., 10 to 12 ppm free phenol deleteriously affects skin and respiratory organs and this is principally attributed to the free phenol. The phenol-formaldehyde resins have the added disadvantage of being relatively more costly than many of the alternative resins such as urea-formaldehyde/melamine resins.
In respect to still other binders for wood materials, e.g., molding materials, U.S. Pat. Nos. 2,629,703 and 2,634,249 teach binders obtained by co-condensing phenolic and ketonic formaldehyde resin solutions wherein the ketonic formaldehyde resins are present in the proportion of from 50 to 95 percent, preferably from 70 to 90 percent by weight.
Still further, according to French Pat. No. 1,270,535, a binder for thermosetting laminates is obtained by first condensing acetone with formaldehyde in alkaline solution and then producing a co-condensate by adding phenol and further amounts of formaldehyde thereto. Unfortunately, the wood materials produced with these phenol-ketone-formaldehyde resin solutions, although avoiding many of the aforementioned disadvantages associated with other binders, do not have the weather resistance required by DIN Standards No. 68,761. Further, the storage stability of these phenol-ketone-formaldehyde co-condensates is unsatisfactory.
One object of the invention is to provide a process and resulting product therefrom wherein the aforementioned disadvantages of the phenol-ketone-formaldehyde binders can be avoided.